This invention relates generally to vapor compression systems and, more particularly, to detection of a loss of refrigerant in a refrigerant vapor compression system.
Conventional vapor compression systems typically include a compressor, a heat rejection heat exchanger, a heat absorption heat exchanger, and expansion device, commonly an expansion valve, disposed upstream with respect to working fluid flow, of the heat absorption heat exchanger and downstream of the heat rejection heat exchanger. These basic system components are interconnected by working fluid lines in a closed circuit, arranged in accord with known vapor compression cycles.
In some vapor compression systems, capacity modulation capability may be added by incorporating a flash tank economizer into the working fluid circuit between the heat rejection heat exchanger and the evaporator. In such case, the working fluid leaving the heat rejection heat exchanger is expanded through an economizer expansion device, such as a thermostatic expansion valve or an electronic expansion valve, prior to entering the flash tank wherein the expanded fluid separates into a liquid component and a vapor component. The vapor component is thence directed from the flash tank into an intermediate pressure stage of the compression process of a multi-stage compression device, while the liquid component is directed from the flash tank through the system's main expansion valve prior to entering the evaporator.
Refrigerant vapor compression systems are commonly used for conditioning air to be supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression system are also commonly used for refrigerating air supplied to display cases, merchandisers, freezer cabinets, cold rooms or other perishable/frozen product storage areas in commercial establishments. Refrigerant vapor compression systems are also commonly used in transport refrigeration systems for refrigerating air supplied to a temperature controlled cargo space of a truck, trailer, container or the like for transporting perishable/frozen items by truck, rail, ship or intermodal.
Refrigerant vapor compression systems used in connection with transport refrigeration systems are generally subject to more stringent operating conditions than in air conditioning or commercial refrigeration applications due to the wide range of operating load conditions and the wide range of outdoor ambient conditions over which the refrigerant vapor compression system must operate to maintain product within the cargo space at a desired temperature. The desired temperature at which the cargo needs to be controlled can also vary over a wide range depending on the nature of cargo to be preserved. The refrigerant vapor compression system must not only have sufficient capacity to rapidly pull down the temperature of product loaded into the cargo space at ambient temperature, but also operate efficiently at low load when maintaining a stable product temperature during transport. Additionally, transport refrigerant vapor compression systems are subject to cycling between an operating mode and standstill mode, i.e. an idle state.
In all refrigerant vapor compression systems, the system must be filled with a refrigerant in an amount sufficient to ensure an adequate amount of refrigerant within the system, commonly referred to as the refrigerant charge, under all operating conditions. An inadequate refrigerant charge can reduce system performance and can lead to system malfunction and damage to system components such as the compressor. It is possible for the refrigerant charge in the system to be initially too low due to human error in filling the system with refrigerant at the manufacturing site or during field installation. It is also possible for the refrigerant charge to be reduced during operation of the system due to leaks which, if undetected and unaddressed, result in the refrigerant charge dropping low enough that system performance is adversely affected and system components damaged.